Plastic closures for many types of beverage, food, juice, pharmaceutical and like applications include a plastic shell that has a lip extending radially inwardly from the closure skirt at a position adjacent to but spaced from the inside surface of the closure shell base wall. A sealing liner is compression molded in situ on the inside surface of the closure base wall, with the lip cooperating with compression mold tooling to form the mold cavity. U.S. Pat. Nos. 4,984,703 and 6,660,349 illustrate closures of this type. It has been proposed to provide vent passages in the liner compression mold tooling to vent air from the mold cavity as the liner is being molded. However, passages in the liner compression mold tooling can become clogged or obstructed, preventing proper ventilation of the mold cavity and leading to entrapment of air bubbles in the liner. This, in turn, undesirably increases the production scrap rate and therefore the cost of producing the closures. It is a general object of the present invention to provide a closure in which the liner compression mold cavity is vented through the closure shell rather than through the mold tooling, thereby enhancing the venting of air from the mold cavity, reducing or eliminating entrapment of air bubbles in the liners, and reducing the closure scrap rate and the cost of production.
A closure shell in accordance with one aspect of the invention includes a base wall with a skirt for securement to a container finish, a lip that extends radially inwardly from the skirt at a position adjacent to but spaced from the base wall, and at least one passage that extends through the lip. In the preferred embodiment of the invention, the passage is in the form of a channel that opens at a radially inner edge of the lip and at axially spaced surfaces of the lip. The channel preferably has a radially inwardly facing surface that angles axially away from the base wall and radially inwardly from the skirt. The lip preferably has a surface that faces axially away from the base wall, with at least a portion adjacent to a radially inner edge of the lip that is flat and perpendicular to the axis of the skirt. The channel preferably opens at this flat portion of the axially facing lip surface.
A plastic closure in accordance with another aspect of the presently preferred embodiment of the invention includes a shell having a base wall with a skirt for securement to a container finish and a lip that extends radially inwardly from the skirt at a position adjacent to and spaced from the base wall. A liner is compression molded in situ against the base wall, and between the base wall and the lip. The lip has a plurality of circumferentially spaced passages that extend through the lip for venting air during compression molding of the liner.